Optical in situ measurements of temperature and layer thickness in Si molecular beam epitaxy

We report on optical in situ measurements of temperature and thickness in silicon molecular beam epitaxy (MBE) by a combination of pyrometry and reflectometry. This method is able to respond to fast temperature changes on the wafer in real-time, and is sensitive enough to monitor even small temperature variations (less than 1°C). We investigate the influence of different MBE components and system operations on the wafer temperature, such as hot cells, electron beam evaporator and LN 2 cooling, etc. The in situ thickness measurements succeeded only for layers thicker than a quarter wavelength ( 60nm). An attempt to measure the optical constants and layer thickness in real-time by fitting the oscillating reflectivity signal during SiGe layer deposition failed due to a poor signal-to-noise ratio, caused by wafer wobbling, scattered light from hot cells and other sources. The optical constants of different SiGe layers were determined after deposition.